To improve the resolution and the sensitivity of optical metrology an interferometer for VUV wavelengths was realized. To examine the influence of the wavelength especially with regard to the period of the object structure, an apochromatic design was chosen. This means an object can be measured with wavelength from 157nm up to 900nm without changing the optical setup. The design of this interferometer will be presented. The benefits and also the technological problems which come along with the use of VUV wavelengths are discussed. Further problems occur when deep binary structures are measured. An overview of those problems will be given and the use of white light interferometric methods to overcome those problems will be discussed. Measurements have been performed with different light sources. The wavelength scale is extended from the visible to the deep UV, the coherence properties of the sources are very dissimilar and the interferograms are evaluated with different techniques. The experimental results will be presented and discussed.